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Ground Fault Current At Main Service
Here's a weird one. I have a tenant with a 150A, 3-Phase, 480V service. The main switchboard is in the basement and the breaker panel is located in the tennant's space 50 feet away. There is also a 120/208 panel board next to the 277/480 volt panel in the same closet. The step-down transformer is suspended above.
Twice in the same year faulty HVAC equipment (480V 3PH) has grounded out and instead of tripping the branch circuit breaker, blows the main fuses in the basement. Once it was a 30 amp A/C device, the second time 9 months later it was a 60 amp duct heater. Again, neither time did the branch circuit breaker(s) trip, instead the main fuses blew. I don't suspect that the circuit breakers (newish) could be faulty although I have not had them tested. Could there be a grounding/neutral issue that is causing this problem... or possibly something else other than faulty breakers? Thanks. |
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